1. Field of the Invention
The present invention relates to a power supply unit, and more particularly, to a power supply unit mounted in a vehicle having an electric motor as a drive source.
2. Description of the Background Art
Generally in a vehicle such as an electric vehicle (EV) or a hybrid vehicle (HV), driving force by electric energy is obtained by converting direct current (DC) electric power supplied from a high-voltage battery into three-phase alternating current (AC) electric power by an inverter and using the converted electric power to rotate a three-phase AC motor. In contrast, when the vehicle slows down, regenerative energy obtained by regenerative power generation in the three-phase AC motor is charged into the battery, and thus the vehicle runs without wasting energy.
Since a nickel metal hydride battery, a lithium ion battery or the like is mainly used as such a battery, reaction heat is generated by chemical reaction when the battery is charged, causing an increase in the temperature of the battery. The increase in the battery temperature results in deterioration of the performance and life of the battery. Therefore, means for cooling the battery is required to suppress the increase in the battery temperature.
For this reason, the vehicle is equipped with a cooling fan for cooling the battery. According to a battery temperature adjusting device mounted in an electric vehicle described in Japanese Patent Laying-Open No. 10-252467, a battery pack holding within a casing a battery assembly having a plurality of batteries is placed in a luggage space in a rear portion of the vehicle. Air which has been used for air conditioning of a cabin is introduced into the battery pack through an introducing passage to cool down or warm up the battery assembly. Further, the air which has been used for cooling down or warming up the battery assembly is exhausted out of the vehicle through an exhausting passage extending from the battery pack to the outside of the vehicle. With this structure, the air which has been used for the air conditioning of the cabin is used to cool down or warm up the batteries, improving heat utilization efficiency using waste heat.
Further, in addition to the high-voltage battery, the vehicle is equipped with an auxiliary battery supplying electric power to auxiliary electric components such as a lighting device, an ignition device, an electric pump, and the like. The auxiliary battery is charged with electric power generated by an alternator, or with electric power from the battery. In particular, when the auxiliary battery is charged with the electric power from the battery, the voltage is down-converted by a DC/DC converter.
It is common that the DC/DC converter connected to the battery, a battery electrical control unit (ECU) controlling charging/discharging of the battery, a sensor detecting the battery temperature, and the like are placed close to the battery pack to reduce wiring resistance between the battery and these components. As an example, these components are all accommodated into a casing and placed close to the battery pack as shown in FIG. 8. Hereinafter, a casing integrally accommodating a variety of circuit components connected to the battery will also be referred to as a “component box”.
FIG. 8 is a perspective diagram of a vehicle equipped with a typical power supply unit.
Referring to FIG. 8, the power supply unit includes a battery pack 100 accommodating a battery group having a plurality of battery cells, and a component box 110 integrally accommodating a DC/DC converter, a battery ECU, a sensor, and the like connected to the battery group. It is to be noted that the direction indicated by an arrow UPR in FIG. 8 shows the direction toward the ceiling of the vehicle (upward direction), the direction indicated by an arrow FR shows the forward direction (moving direction) of the vehicle, the direction indicated by an arrow LH shows the direction toward the left side of the vehicle (left-side direction), and the direction indicated by an arrow RH shows the direction toward the right side of the vehicle (right-side direction).
Battery pack 100 has a shape for example of a rectangular box, and is placed on the floor of a luggage space 6 located behind a rear seat 5.
Component box 110 is placed adjacent to battery pack 100 in the direction indicated by arrow LH. Component box 110 and battery pack 100 are electrically connected with wiring (not shown). To ensure accommodating capacity of luggage space 6, battery pack 100 and component box 110 preferably have a small volume in total. Accordingly, in the case where battery pack 100 and component box 110 are placed in a line in the direction indicated by arrow LH as shown in FIG. 8, the volume of luggage space 6 can be ensured, and its accommodating capacity can also be enhanced by reclining rear seat 5 to spatially connect a cabin to luggage space 6.
It is to be noted that the DC/DC converter accommodated in component box 110 requires cooling because heat is generated by a power element. Thus, component box 110 further includes a cooling fan for cooling the DC/DC converter therein.
Recently, there has been a tendency that, to serve a need for higher-power vehicles, batteries have further been improved to have a higher voltage, resulting in an increase in the number of battery cells. The increase in the number of battery cells leads to an increase in the volume of battery pack 100 on a proportional basis.
When the tendency of higher-voltage batteries is applied to a conventional power supply unit, the increase in the volume of battery pack 100 is limited due to the limited volume of a portion in which the power supply unit can be mounted in the direction indicated by arrow LH in the vehicle, as shown in FIG. 8. Although dividing the battery group within battery pack 100 and separately placing the divided battery subgroups can be considered as one solution to attain a higher-voltage battery, the solution is not appropriate because it requires a space and cost for placing each of the divided battery subgroups.
Further, in the conventional power supply unit, component box 110 is placed adjacent to battery pack 100 in the direction indicated by arrow LH, as shown in FIG. 8. Accordingly, among the plurality of batteries constituting the battery group, a battery located on one side adjacent to component box 110 exchanges heat with component box 110 due to a difference in casing temperatures, and thus the battery comes to have a temperature different from that of a battery located on the other side. Consequently, variations in temperature are caused in the battery group in the direction indicated by arrow LH in FIG. 8, which may result in variations in characteristics and lives of the batteries.